1. Field of the Invention
The present invention relates to a forming phase alignment device in a formed sheet manufacturing apparatus, and particularly to a forming phase alignment device which aligns phases of a front and back of an optical high-precision double-surface formed sheet formed by an extrusion forming method.
2. Description of the Related Art
Forming of an optical high-precision double-surface formed sheet, in which irregularity patterns are formed on both front and back surfaces, such as a lenticular plate for use in a screen for a rear projector, is performed by an extrusion forming method by using a formed sheet manufacturing apparatus in which two forming rolls having patterns carved on outer circumferential surfaces are provided parallel and opposite to each other.
This formed sheet manufacturing apparatus includes one constructed to be capable of moving one of the forming rolls making a pair in a roll axis direction, that is, a sheet width direction by a phase adjustment mechanism driven by a servo motor in order to align forming phases of the front and back of the double-surface formed sheet in the roll axis direction (for example, refer to Japanese Patent Laid-Open Publication No. 2004-142182).
In the formed sheet manufacturing apparatus, periodic variations in one rotation of each of the rolls, which affect phase precision in the roll axis direction (a thrust direction), occur owing to precision of rotational mechanical parts constructing the formed sheet manufacturing apparatus, precision in the thrust direction, which is owned by the rolls themselves carved for the purpose of the forming, and the like.
In the phase adjustment mechanism in the formed sheet manufacturing apparatus in the related art, though adjustment of positional precision of the mechanism itself in the roll axis direction is accurate, information on actual forming precision of the front and back of such a product formed by the manufacturing apparatus is not included in control factors. Therefore, in the related art, further high-precision forming required for a final product is difficult.
In the optical high-precision double-surface forming by the extrusion forming method, a range of temperature set for the forming rolls for the purpose of the forming is widened owing to specifications of the product, a type of resin, a type of the forming patterns, and the like. For example, the temperature is set at 80° C. to 120° C. Moreover, a range of roll thrust conditions for the purpose of the forming is also widened. Accordingly, in order to cover such wide forming conditions, a range of force required for adjusting the phases of the forming rolls in the axial direction is also widened.
An option to select the mechanism for the purpose of mechanically clearing the conditions as described above is also limited, and variations of the selected mechanism in the thrust direction essentially occur. As the variations of the selected mechanism in the thrust direction, for example, ±4 μm is mentioned, which is present even in a high-precision thrust bearing. Moreover, in an actual machine, periodic variations in the thrust direction in terms of forming displacement are present in the case of processing the forming rolls as other bodies of rotation, resulting in compound variations of the bodies of rotation.
In such a control method at present, the information on the forming variations of the final product is not included, and accordingly, an influence of the compound variations of the bodies of rotation will appear on the product.